Geochemical Characteristics of Ophiolites in Yongzhu-Guomangcuo, Tibet and Its Tectonic Significance

Ophiolites exposed from Yongzhu to Guomangcuo are mainly composed of metamorphic harzburgites,gabbros and basalts.From the analysis of major and trace elements of ophiolites in Yongzhu-Guomangcuo,the (characteristics) of its metamorphic harzburgites are high Mg content,and lower in Ti and ∑REE,and belong to the depleted oceanic lithosphere mantle.The diabases and basalts are the transitional MORB/IAB-type basalt.According to the trace elements in the ophiolite,the gabbros and basalts show the same characteristics as the island arc basalt,for the depletion elements of Nb,Ta and its relative enrichment of Rb,Sr and Ba.Meanwhile,according to the REE distribution patterns with no Eu anomaly,the gabbros and basalts are similar to mid-ocean ridge basalt.It is concluded that the geotectonic setting of ophiolite of Yongzhu is formed in back arc basin by the comparison with the ophiolite of typical areas and discrimination diagrams of the tectonic setting.This indicates that ophiolite complex of Yongzhu has a more complex evolution history than hitherto considered.